Air moving across an array of photovoltaic (PV) assemblies mounted to the roof of a building, or other support surface, creates wind uplift forces on the PV assemblies. Much work has been done in the design and evaluation of arrays of PV assemblies to minimize wind uplift forces. See U.S. Pat. Nos. 5,316,592; 5,505,788; 5,746,839; 6,061,978; and 6,148,570. Reducing wind uplift forces provides several advantages. First, it reduces the necessary weight per unit area of the array. This reduces or eliminates the need for strengthening the support surface to support the weight of the array, thus making retrofit easier and reducing the cost for both retrofit and new construction. Second, it reduces or eliminates the need for the use of roof membrane- (or other support surface-) penetrating fasteners; this helps to maintain the integrity of the membrane. Third, the cost of transporting and installing the assembly is reduced because of its decreased weight. Fourth, lightweight PV assemblies are easier to install than assemblies that rely on ballast weight to counteract wind uplift forces. Fifth, when designed properly, the assembly can serve as a protective layer over the roof membrane or support surface, shielding from temperature extremes and ultraviolet radiation.
Various aspects of the invention are based upon the discovery and recognition that (1) wind uplift forces are spatially distributed, both dynamically and randomly, so that wind uplift forces on a particular PV assembly within an array of PV assemblies changes rapidly in magnitude; and (2) interengaging the various PV assemblies within an array of PV assemblies causes wind uplift forces acting on a single PV assembly to be transferred to other, typically adjacent, PV assemblies.
A first aspect of the invention is directed to an array of pressure-equalizing photovoltaic (PV) assemblies mountable to a support surface. Each PV assembly comprises a base, a PV module and a support assembly securing the PV module to a position overlying the upper surface of the base. Vents are formed through the base. A pressure equalization path extends from the outer surface of the PV module, past the peripheral edge of the PV module, to and through at least one of the vents, and to the lower surface of the base. This provides pressure equalization between the outer surface of the PV module and the lower surface of the base to help reduce wind uplift forces on the PV assembly. The vents may be generally aligned or coincident with the peripheral edge. At least a portion of the path extending from the peripheral edge to at least one of the vents may be an unobstructed path portion. At least one of the vents may be positioned between the outer edge of the base and the support assembly. The base may include an electrical conductor, typically in the form of a metal cover, and further may include electrical ground connectors between the electrical conductors. The PV assemblies may be interengaged, such as by interengaging the bases of adjacent PV assemblies. The base may include a main portion and a cover and the bases of adjacent PV assemblies may be interengaged by securing the covers of adjacent bases together. The PV module may be an inclined PV module and the support assembly may be a multi-position support assembly which secures the PV module at shipping and inclined-use angles. The array may also include a deflector and a multi-position deflector support securing the deflector to the base at shipping and inclined-use angles. At least one of the vents may be generally vertically aligned or coincident with a gap defined between opposed portions of the inclined PV module and deflector; a conduit may fluidly couple the gap and at least one of the vents. The array maybe circumscribed by a perimeter assembly; the perimeter assembly may include perimeter elements. The perimeter elements are typically secured to one another and to the adjacent PV assemblies. Cross strapping, extending above, below or through the array, or some combination of above, below and through the array, may be used to secure one perimeter element to a non-adjacent perimeter element.
A second aspect of the invention is directed to a PV system comprising a support surface and an array of pressure-equalizing photovoltaic (PV) assemblies mounted to the support surface. Each PV assembly comprises a base, a PV module and a support assembly securing the PV module to a position overlying the upper surface of the base. Vents are formed through the base. A pressure equalization path extends from the outer surface of the PV module, past the peripheral edge of the PV module, to and through at least one of the vents, and to the lower surface of the base. This provides pressure equalization between the outer surface of the PV module and the lower surface of the base to help reduce wind uplift forces on the PV assembly. The peripheral edges of adjacent PV assemblies are separated by an average distance of about d. The support surface may comprise a surface with alternating ridges and troughs. Filler elements may be used within the troughs beneath the array of PV assemblies.
A third aspect of the invention is directed to a PV assembly, for use on a support surface. Each PV assembly comprises a base, a PV module and a module support assembly securing the PV module to a position overlying the upper surface of the base. The PV module is oriented at a first angle to the base by the module support and a deflector is oriented at a second angle to the base by a deflector support. Portions of the PV module and deflector define a gap therebetween. Vents are formed through the base. A pressure equalization path extends from the outer surface of the PV module, through the gap, to through at least one of the vents and to the lower surface of the base. This provides pressure equalization between the outer surface of the PV module and the lower surface of the base to help reduce wind uplift forces on the PV assembly. The module support and the deflector support may be multi-position module and deflector supports to support the module and deflector at shipping and inclined-use angles relative to the base. At least one conduit may fluidly couple the gap and at least one of the vents. The portion of the pressure equalization path between the gap and vent is a direct, unobstructed path; the path portion may also be a constrained leakage path portion which may be at least partially defined by the module support assembly.
A fourth aspect of the invention is directed to a PV system comprising a support surface, comprising alternating ridges and troughs, and an array of pressure-equalizing photovoltaic (PV) assemblies mounted to the support surface. Each PV assembly comprises a base, a PV module and a support assembly securing the PV module to a position overlying the upper surface of the base. A vent is formed through the base between the center of the PV module and the support assembly. A pressure equalization path extends from the outer surface of the PV module, past the peripheral edge of the PV module, to through the vent and to the lower surface of the base. This provides pressure equalization between the outer surface of the PV module and the lower surface of the base to help reduce wind uplift forces on the PV assembly. Filler elements may be used within the troughs beneath the array of PV assemblies. A second vent may be formed through the base at a position generally aligned or coincident with the peripheral edge. Thermal insulation may be located within the troughs between the lower surface of the base and the support surface. A perimeter assembly may be used to circumscribe the array of PV modules.
A fifth aspect of the invention is directed to a method for reducing wind uplift forces on an array of pressure-equalizing photovoltaic (PV) assemblies mountable to a support surface. Each PV assembly comprises a base, a PV module and a support assembly securing the PV module to a position overlying the upper surface of the base. The method comprises forming vents through the base and creating a pressure equalization path extending from the outer surface of the PV module, past the peripheral edge, to and through at least one of the vents, and to the lower surface of the base. At least some of the vents may be positioned to be generally aligned or coincident with the peripheral edge. The pressure equalization path may be created so that the portion of the path extending from the peripheral edge to a vent is an unobstructed path portion. The PV module may be oriented at an angle to the base and a deflector may be mounted at an angle to the base, the module and deflector having portions defining a gap therebetween. At least one hollow conduit may be used to fluidly couple the gap and a vent.
A sixth aspect of the invention is directed to a method for reducing wind uplift forces on an array of pressure-equalizing photovoltaic (PV) assemblies mountable to a support surface comprising alternating ridges and troughs. Each PV assembly comprises a base, a PV module and a support assembly securing the PV module to a position overlying the upper surface of the base. The method comprises forming vents through the base and creating pressure equalization paths extending from the outer surface of the PV module, past the peripheral edges, to and through at least one of the vents, and to the lower surface of the base. The method may also comprise substantially filling the troughs beneath the array of PV assemblies, such as with insulation. At least one of the vents may be positioned at a location between the center of the PV module and the support assembly for each of a plurality of the PV modules.
The provision of the vents in the base of the PV assembly provides for pressure equalization to reduce or eliminate wind uplift forces. Appropriately positioning the array on the roof of a building also helps to reduce wind uplift forces. Reducing wind uplift forces provides several advantages. First, it reduces the necessary weight per unit area of the array. This reduces or eliminates the need for strengthening the support surface to support the weight of the array, thus making retrofit easier and reducing the cost for both retrofit and new construction. Second, it reduces or eliminates the need for the use of roof membrane- (or other support surface-) penetrating fasteners; this helps to maintain the integrity of the membrane. Third, the cost of transporting and installing the assembly is reduced because of its decreased weight. Fourth, lightweight PV assemblies are easier to install than assemblies that rely on ballast weight to counteract wind uplift forces. In addition, using a PV assembly comprising a base permits the PV assembly to help protect the support surface from the effects of sun, wind, rain, etc., and also, when the base comprises thermal insulation, increases the thermal insulation qualities of the support surface. Further, the interengagement of the PV assemblies, and the maintenance of the interengagement of the PV assemblies, helps to ensure that uplift forces on one PV assembly tends to get transferred to adjacent PV assemblies thereby helping to counteract wind uplift forces.
Other features and advantages of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings.